let X, Y, Z, V be set ; :: thesis: ( X c= Y & Z c= V implies X \ V c= Y \ Z )
assume ( X c= Y & Z c= V ) ; :: thesis: X \ V c= Y \ Z
then ( X \ V c= Y \ V & Y \ V c= Y \ Z ) by Th33, Th34;
hence X \ V c= Y \ Z ; :: thesis: verum